The present invention relates to latch assemblies, in particular latch assemblies for use with car doors and car boots.
Latch assemblies are known to releasably secure car doors in a closed position. Operation of an inside door handle or an outside door handle will release the latch, allowing the door to open. Subsequent closure of the door will automatically relatch the latch.
In order to ensure that rain does not enter the vehicle, the doors are provided with weather seals around their peripheral edge which close against an aperture in the vehicle body in which the door sits. In addition to providing protection from rain, the weather seals also reduce the wind noise. The ongoing requirement for improved vehicle occupant comfort requires minimizing of wind noise, which in turn requires the weather seals to be clamped tighter by the door. The door clamps the seals by virtue of the door latch, and accordingly there is a tendency for the seal load exerted on the latch to be increased in order to meet the increased occupancy comfort levels required. Because the seal forced on the latch is increased, then the forces required to release the latch are correspondingly increased.
U.S. Pat. No. 3,386,761 shows a vehicle door mounted latch having a rotatable claw which releasably retains a vehicle body mounted striker to hold the door in a closed position. The claw is held in the closed position by a first pawl (which is a tension pawl). The first pawl is held in the closed position by a second pawl. The second pawl can be moved to a release position by an electric actuator which in turn frees the first pawl to rotate counter-clockwise, which allows the claw to rotate clockwise to the open position.
The system is arranged such that once the second pawl has disengaged the first pawl, the first pawl is driven to a release position by the seal load acting on the claw.
US2004/0227358 shows a rotatable claw held in the closed position by a rotatable lever and a link. The rotatable lever can in turn be held in position by a pawl (which is a compression pawl). Disengaging the pawl from the lever (by rotating it clockwise) allows the lever, the link and the pawl to move to an open position. In particular, the link rotates in a clockwise direction. One end of the link remains in permanent engagement with the claw. The system is arranged such that once the pawl has disengaged from the lever, the lever and the link are driven to the open position by the seal load acting on the claw.
EP0978609 shows a rotatable claw that can be held in a closed position by a compression pawl. The pawl is mounted on a cam and during an initial part of opening of the latch, the cam rotates relative to the pawl, thereby initially slightly increasing and then significantly reducing the seal load. During the final part of opening of the latch, the cam and the pawl rotate clockwise in unison, thereby disengaging the pawl tooth from the claw tooth which allows the claw to rotate clockwise to the open position. However, the arrangement is such that the cam must be driven by a motor to release the latch. In particular, in the closed position, the particular configuration of the cam axis, the pawl pivot axis and the pawl tooth is such that the latch will remain shut. Thus, in the closed position, the pawl pivot axis (28 of EP0978609) lies just to one side of a line (31 of EP0978609) drawn between the cam axis and the point where the pawl tooth contacts the claw. Significantly, the pawl pivot axis must initially move towards this line in order for the latch to be opened, and it will be appreciated that a locus defined by movement of the pawl pivot axis during opening crosses this line. In other words, the pawl is at an over-center position, such that the cam is biased in a closing direction (counter-clockwise in this case) by the pawl when the latch has been closed, whereas the cam must be driven in an opening direction (clockwise in this case) to open the latch.
DE10214691 is similarly in an overcenter position when in the closed position. Similarly, the pawl pivot axis must initially move towards the line equivalent of line 31 of EP0978609, and similarly a locus defined by the pawl axis during opening of the latch crosses this line. DE10214691 shows a compression pawl which must be rotated counter-clockwise to disengage the claw, thereby allowing the claw to rotate counter-clockwise to release the striker.
U.S. Pat. No. 5,188,406 shows an example of a latch having a tension pawl (FIG. 2) and a further example of a latch showing a compression pawl. The tension pawl 6 is pivotally mounted on a link 5, which in turn is pivotally mounted on the latch body. As can be seen from FIG. 2 of this patent, the pivot axis of the link 5 with the latch body, the pivot axis between the pawl 6 and the link 5, and the point of contact between the pawl 6 and latch bolt 3 all lie on a straight line. During opening, the pivot axis between the pawl 6 and the link 5 moves clockwise and then counter-clockwise, and in doing so crosses the above mentioned straight line. The pawl must rotate counter-clockwise to disengage the rotating latch bolt 3, which then can rotate clockwise to release the striker. The example of the latch shown in FIG. 4 of this patent is a compression pawl which operates in a similar manner. However, in this case, the pawl must rotate clockwise to disengage the claw which then also rotates clockwise to allow the striker to be released.
U.S. Pat. No. 4,988,135 shows a tension pawl mounted on an eccentric. A pin 28 secured to the pawl proximate the pawl tooth but remote from the eccentric is limited in its movement by an enlargement 38 of the pin 28 contacting a stop 37. The pawl must be rotated clockwise to disengage it from the claw which then rotates counter-clockwise to release the striker.
Thus EP0978609, DE10214691, U.S. Pat. Nos. 5,188,406 and 4,988,135 all show latches in which the component in direct contact with the claw (the pawl) is in a stable position whereas U.S. Pat. No. 3,386,761 and US2004/0227358 both show latches wherein the component in direct contact with the claw is in an unstable position, and therefore requires a further component (the second pawl in U.S. Pat. No. 3,386,761, and the pawl in US2004/0227358) to hold the component that directly engages the claw in its unstable position.
It will be appreciated from the above explanation that where a latch has a compression pawl, the compression pawl rotates in the same direction as the claw (or in the same direction as the lever of US2004/0227358) to release the latch, whereas when a latch includes a tension pawl, the tension pawl must be rotated in the opposite direction to the claw. Thus, U.S. Pat. Nos. 3,386,761, 4,988,135 and FIG. 2 of U.S. Pat. No. 5,188,406 all show tension pawls, whereas EP0978609, DE10214691, US2004/0227358 and FIG. 4 of U.S. Pat. No. 5,188,406 all show compression pawls.